The present invention generally relates to devices having at least one torsional hinge, and more particularly to MEMS (micro-electro mechanical systems) optical devices with movable mirrors and motion stops for limiting undesirable translational motion of such mirrors.
In recent years optical fibers have come into wide spread use in a wide variety of applications in which optical signals are transmitted along such fibers and are switched from one optical fiber to another using an optical switch system. Optical switches generally include structure to support fiber positioning, alignment signal emitters and interconnected computer control electronics. A fiber positioning structure is provided near the end of each fiber to selectively point the end of a fiber to one fiber group toward the end of a selected fiber in another fiber group to provide switched optical transmission between the two fibers. Examples of optical switches are shown in U.S. Pat. Nos. 4,512,036 and 5,177,348.
Movable mirrors having torsional hinges may be used as the switching device in such optical switching systems to reflect, route, and/or attenuate light of the optical signals. This type of mirror may also be used for many other purposes. However, the durability and life span of current torsion-hinge movable mirror devices have suffered due to failures in the torsional hinge which allows pivoting of the devices. Such failures are at least partly because the torsional hinge mirror devices often experience translational motion in the mirror surface plane due to vibrations and/or shock during manufacturing, handling, and shipping. In other words, translational movement of the mirror element in the plane of the mirror surface may cause a hinge of the movable mirror device to experience bending and/or shear forces in directions other than the generally intended rotation (e.g., for tilting the mirror element during intended use of the device). Since unwanted or unintended forces are often the cause of failure for these devices, there is a need for reducing or eliminating such unwanted or unintended forces experienced by the hinges of a torsion-hinge movable mirror device.
Texas Instruments presently manufactures a two-axis analog mirror MEMS device fabricated out of a single piece of material (such as silicon, for example) typically having a thickness of about 100-115 microns. The layout consists of a mirror (normally about 3.8 mmxc3x973.2 mm) supported on a gimbal frame by two silicon torsional hinges. The gimbal frame is attached to a support frame by another set of torsional hinges. A similar single axis mirror MEMS device may be manufactured by eliminating the gimbal frame, and extending the mirror torsional hinges directly to the support structure.
The problem of translational motion and forces exerted on a torsional hinge may also exit in devices other than movable mirror devices. Hence, there is generally a need for a way to reduce or eliminate unwanted or unintended translational motion and forces experienced by a torsional hinge in these devices.
The problems mentioned above are addressed by the present invention, which according to one embodiment, provides a device having a movable structure. The movable structure includes a frame portion and a movable portion, such as a mirror, which is hinged to the frame portion by a first pair of torsional hinges spaced apart along an axis, such that the movable portion can pivot about the axis relative to the frame portion. The movable portion has at least one edge that is substantially perpendicular to the axis and substantially parallel with and immediately adjacent to a corresponding edge of the frame portion. The two substantially parallel edges are spaced a small distance apart, and at least one projection extends from one or both of the edges into the spaced defined by these two substantially parallel edges. The projection is adapted to limit relative translational motion between the movable portion and the frame portion. According to another embodiment, similar spaces perpendicular to the axis are defined proximate both torsional hinges with each space having at least one projection extending into the space from one of the two parallel edges. Still another embodiment may include a pair of spaces with their corresponding projections located on each side of one or both of the torsional hinges.
In accordance with another aspect of the present invention, an optical device is provided having a structure similar to that discussed above wherein the movable portion is a mirror formed from a single piece of substantially planar material.
According to still another embodiment, the optical device may be an inner mirror portion having a reflective mirror surface formed thereon, and may further comprise another or second movable portion. The second movable portion may be hinged to the first mentioned movable portion by another set or pair of hinges spaced apart along a second axis in the plane, such that the second movable portion can pivot relative to the first mentioned movable portion about the second axis. A reflective mirror surface may be formed on the second movable portion to form an inner mirror, wherein the first movable portion is an intermediate gimbals portion. In a manner similar to that discussed above, a projection may extend from one or both of an edge of the second movable portion which is perpendicular to the second axis or a corresponding second edge of the first movable portion, which is parallel to the edge of the second movable portion. The projection again extends within a space formed between the second edge of the first movable portion and the corresponding parallel edge of the second movable portion. In the same manner as discussed above, this projection is also adapted to limit translational motion of the second movable portion relative to the first movable portion. According to one embodiment, the first axis will be substantially perpendicular to the second axis.